1. Field of the Invention
This invention relates to signaling devices useful with an instrument or tool having a pointer and indicating plate. More particularly, this invention relates to a signaling device for indicating that a predetermined torque has been applied to a conventional torque wrench.
2. Description of the Prior Art
In the measuring arts, there are numerous tools and instruments which use a pointer and an indicator plate. Commonly, the pointer will rotate or otherwise move along the indicator plate, thereby pointing to indicia representing values of the measured variable. Among these instruments, are such devices as a gas gauge, a weight scale, and a torque wrench.
One of the disadvantages of such pointer in indicating plate instruments is that they are sometimes used in places where it is very hard, if not impossible, to see where the pointer arm is pointing to on the indicator plate. At other times, one can see generally where the pointer is pointing to but, because of the angle one is viewing the indicator plate at, parallax error is introduced. This problem of not being able to view the indicator plate directly is especially troublesome when using a torque wrench, where one often has to work at unusual angles or in unusual positions.
It is therefore useful to have a device which indicates when a pointer has been deflected a certain amount, thus avoiding the necessity of having a direct view of the indicating plate.
The following U.S. Patents include various devices for overcoming the necessity of direct viewing of an indicator plate:
Jones U.S. Pat. No. 625,843 PA0 Charland U.S. Pat. No. 843,929 PA0 Wood U.S. Pat. No. 1,742,229 PA0 Behr U.S. Pat. No. 2,523,352 PA0 Larson et al. U.S. Pat. No. 2,792,734 PA0 Hanscom et al. U.S. Pat. No. 3,142,177 PA0 Kraus U.S. Pat. No. 3,664,186 PA0 Myrdal U.S. Pat. No. 3,967,513 PA0 Smyth U.S. Pat. No. 4,112,749
The Kraus and Larson et al patents show specifically designed torque wrenches, wherein the mechanic need not have a direct view of the indicating plate for correctly using them. However, these devices are of little use to a mechanic who does not wish to purchase a completely new torque wrench. The Behr patent similarly shows a pointer activated indicating device which requires that one replace one's present gas gauge. That is, like Larson and Kraus, the use of the Behr device requires one to replace one's presently owned pointer and indicating plate tool or instrument. These devices are thus incapable of use with one's present pointer and indicating plate instrument.
The Smyth and Myrdal patents show pointer activated indicating devices for torque wrenches wherein the device must be slid up and down the length of the torque beam. This is disadvantageous in that it is hard to position the sliding unit in a position corresponding to the predetermined amount of torque desired, unless one uses a workpiece to apply that degree of torque. Alternately, Smyth discusses adding calibrations along the length of the wrench in order to enable the user to set the device.
The Charland and Wood patents both show sliding units which have two contacts. The sliding unit is positioned along the indicating plate at a point corresponding to a predetermined value. When the pointer reaches the place where the sliding unit is positioned, the pointer will connect the two contacts together, thus closing a circuit at least partially removed from the sliding unit. The necessity for having wires extending from the sliding unit makes it more difficult to adapt a conventional pointer and indicating plate instrument.
The Jones patent discloses a pointer triggered alarm device wherein a sliding unit, such as clip 10 of FIG. 1, has one contact. An alternate clip device, such as 12 of FIG. 1, is used for making the pointer a part of the circuit. When the pointer touches clip 10 it closes a circuit, thus ringing a bell 14. In addition to the disadvantage of requiring wires extending off the clips, Jones necessitates the use of at least two clips, one to carry current to the pointer arm, and the other to provide a completed circuit path when the pointer reaches a predetermined value.
The Hanscom patent shows a torque sensing device which slides along a bridge 8 of FIG. 1. In addition to requiring modification of a conventional torque wrench to include a bridge, Hanscom is disadvantageous in that it uses the pointer to trigger a spring device which must then be reset before the next use.
It will then be seen that although the prior art has included many attempts to provide a pointer triggered indicating device, the inventions which have been developed are all subject to one or more disadvantages. Specifically, these devices have required extensive modification of the conventional pointer and indicating plate instrument, necessitated cumbersome wiring removed from a dial plate fastening part, required the operator to reset after each use, or have been difficult and inconvenient to set to the appropriate value.